Short version - Start at the Upper Oso campground way out on Paradise Rd., go up the fire road 11 miles (you'll pass the end of the singletrack descent in the first mile of the fire road). Come to a peak with a bunch of pines. Find the singletrack on the other side and enjoy. Believe it's 3500' of climbing, 7 mile uninterrupted descent.

Different trail. Buckhorn drops off the road on the other side of the mountain about a mile before you hit the turnoff for LP/SC . I don't know for sure, but I'm guessing that it's pretty overgrown right now and when you get down closer to the bottom of the canyon there will be a fair bit of oak (the poison kind).

Buckhorn Trail is not Santa Cruz / Little Pine, this is a much longer loop but the fireroad climb is the same but instead of descending towards the ocean (south-ish) the descent is on the north-ish side of the range and the trailhead is sooner than the Santa Cruz descent.

Maybe 1.5 miles prior to Little Pine campground the Buckhorn trail head starts, as you climb, it is on the right and there is a fairly large sign. Fun descent down that can be really overgrown with Poison Oak if the SBMTV / IMBA guys haven't hacked it back for awhile. There are lots of stream and creak crossings (Indian Creek / Buckhorn Creek), mostly have to Hike a Bike over and sometimes hard to see where the trail is on the other side of the crossings.

People have got lost on this trail so it is not impossible to do, but I think it's at least hard to get lost. I did it alone for the first time 10 years ago and didn't get lost with nothing really to guide me, but you do feel alone! It feels like you are a long way from civilization with lots of snakes and birds and other evidences of animals including mtn lions.

At the end of the singletrack, about 6 miles maybe?, go right and continue on the fireroad which is gated with a hiking sign in sheet. If you turn left you will end up at Gibraltar Dam, don't go left. I believe this road is Camuesa which you passed on the right when you were climbing up from Upper Oso. Just follow this fire road up out of the valley until you come to the T from whence you started. Roll downhill back to Upper Oso. I think the entire round trip was somewhere close to 35 miles.

I rode this a few years back, and I gotta say, it wasn't all that great. We rode the Santa Cruz trail the following day, which was awesome. It's the same climb, just a much more fun descent on Santa Cruz, IMHO. You go all the way down Buckhorn, then get to the bottom, have a long climb out a fireroad, and finish with fireroad descent. Not an epic, in my mind.